[roc-chat] Re: Tether setups

  • From: David Erbas-White <derbas@xxxxxxxxxxxxxxxx>
  • To: roc-chat@xxxxxxxxxxxxx
  • Date: Sun, 17 Jun 2012 11:26:18 -0700

On 6/17/2012 11:05 AM, Jeff Gortatowsky wrote:

Greg thanks that is helpful, all my rockets have been single deploy and I simply test for continuity during prep (no charge, just the match), then cut one lead, strip it, tape over one end of the bare wire, then put the charge in. At the pad I take off the tape, twist the two bare ends together, and place the tape back over it. Now with a larger dual deploy, and to MAYBE use it as an L3 project, I need to change that I guess. So forgive another dumb question...

What is the difference between shunting at the pad, and safeing should it come down in an indeterminate state?
Seems like
1) Shunts are a possible failure point under boost, opening or closing under G load and vibration (depend on what you used of course - maybe that is NOT so?)
2) The screw switches would provide both functions anyway(???)


I'm not Greg, but...

Shunting is good, but not great. Nor is just twisting the wires together, unless you're using something to actually constrict the connection (such as a wire nut). I would also recommend taping the 'screw switch' once you've moved it to the open position (so that a) no foreign material that may be conductive lodges between the screw head and the connetions, and b) so that the screw doesn't "wiggle down" and make contact during both prep and flight, and accidentally short any needed charge for the main).

You'd be surprised how many apparently SOLID connections can be knocked loose with a little G-force. On a (work) project I worked on, we had some EXTREMELY strong clips holding the batteries in place, but would experience intermittent failures of the power supply. Tracing down the problem using the internal time-stamped logs of the device, we determined that these always occurred while the unit was in transit, during shipping. Taking a unit that supposedly had bullet-proof connections and tossing it down the stairs (in it's shipping package) confirmed the hypothesis -- so now all of these connections are either soldered, or using very high-quality pin connectors that grab on all sides, and are positioned such that G-forces won't affect them.

David Erbas-White

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